Fullerenes are closed-cage molecules composed entirely of sp2-hybridized carbons, arranged in hexagons and pentagons. Fullerenes (e.g. C60) were first identified as closed spheroidal cages produced by condensation from vaporized carbon.
Fullerene tubes are produced in carbon deposits on the cathode in carbon arc methods of producing spheroidal fullerenes from vaporized carbon. Ebbesen et al. (Ebbesen I), xe2x80x9cLarge-Scale Synthesis Of Carbon Nanotubes,xe2x80x9d Nature, Vol. 358, p. 220 (Jul. 16, 1992) and Ebbesen et al., (Ebbesen II), xe2x80x9cCarbon Nanotubes,xe2x80x9d Annual Review of Materials Science, Vol. 24, p. 235 (1994). Such tubes are referred to herein as carbon nanotubes. Many of the carbon nanotubes made by these processes were multi-wall nanotubes, i.e., the carbon nanotubes resembled concentric cylinders. Carbon nanotubes having up to seven walls have been described in the prior art. Ebbesen II, Iijima et al., xe2x80x9cHelical Microtubules Of Graphitic Carbon,xe2x80x9d Nature, Vol. 354, p. 56 (Nov. 7, 1991).
Single-wall carbon nanotubes have been made in a DC arc discharge apparatus of the type used in fullerene production by simultaneously evaporating carbon and a small percentage of Group VIII transition metal from the anode of the arc discharge apparatus. See Iijima et al., xe2x80x9cSingle-Shell Carbon Nanotubes of 1 nm Diameter,xe2x80x9d Nature, Vol. 363, p. 603 (1993); Bethune et al., xe2x80x9cCobalt Catalyzed Growth of Carbon Nanotubes with Single Atomic Layer Walls,xe2x80x9d Nature, Vol. 63, p. 605 (1993); Ajayan et al., xe2x80x9cGrowth Morphologies During Cobalt Catalyzed Single-Shell Carbon Nanotube Synthesis,xe2x80x9d Chem. Phys. Lett., Vol. 215, p. 509 (1993), Zhou et al., xe2x80x9cSingle-Walled Carbon Nanotubes Growing Radially From YC2 Particles,xe2x80x9d Appl. Phys. Lett., Vol. 65, p. 1593 (1994); Seraphin et al., xe2x80x9cSingle-Walled Tubes and Encapsulation of Nanocrystals Into Carbon Clusters,xe2x80x9d Electrochem. Soc., Vol. 142, p. 290 (1995); Saito et al., xe2x80x9cCarbon Nanocapsules Encaging Metals and Carbides,xe2x80x9d J. Phys. Chem. Solids, Vol. 54, p. 1849 (1993); Saito et al., xe2x80x9cExtrusion of Single-Wall Carbon Nanotubes Via Formation of Small Particles Condensed Near an Evaporation Source,xe2x80x9d Chem. Phys. Lett., Vol. 236, p. 419 (1995). It is also known that the use of mixtures of such transition metals can significantly enhance the yield of single-wall carbon nanotubes in the arc discharge apparatus. See Lambert et al., xe2x80x9cImproving Conditions Toward Isolating Single-Shell Carbon Nanotubes,xe2x80x9d Chem. Phys Lett., Vol. 226, p. 364 (1994).
While this arc discharge process can produce single-wall nanotubes, the yield of nanotubes is low and the tubes exhibit significant variations in structure and size between individual tubes in the mixture. Individual carbon nanotubes are difficult to separate from the other reaction products and purify.
An improved method of producing single-wall nanotubes is described in U.S. Ser. No. 08/687,665, entitled xe2x80x9cRopes of Single-Walled Carbon Nanotubesxe2x80x9d incorporated herein by reference in its entirety. This method uses, inter alia, laser vaporization of a graphite substrate doped with transition metal atoms, preferably nickel, cobalt, or a mixture thereof, to produce single-wall carbon nanotubes in yields of at least 50% of the condensed carbon. The single-wall nanotubes produced by this method tend to be formed in clusters, termed xe2x80x9cropes,xe2x80x9d of 10 to 1000 single-wall carbon nanotubes in parallel alignment, held together by van der Waals forces in a closely packed triangular lattice. Nanotubes produced by this method vary in structure, although one structure tends to predominate
Although the laser vaporization process produces improved single-wall nanotube preparations, the product is still heterogeneous, and the nanotubes are too tangled for many potential uses of these materials. In addition, the vaporization of carbon is a high energy process and is inherently costly. Therefore, there remains a need for improved methods of producing single-wall nanotubes of greater purity and homogeneity. Furthermore, many practical materials could make use of the properties of single-wall carbon nanotubes if only they were available as macroscopic components. However, such components have not been produced up to now.
Accordingly, it is an object of this invention to provide a high yield, single step method for producing large quantities of continuous macroscopic carbon fiber from single-wall carbon nanotubes using inexpensive carbon feedstocks at moderate temperatures.
It is another object of this invention to provide macroscopic carbon fiber made by such a method.
It is also an object of this invention to provide a molecular array of purified single-wall carbon nanotubes for use as a template in continuous growing of macroscopic carbon fiber.
It is another object of the present invention to provide a method for purifying single-wall carbon nanotubes from the amorphous carbon and other reaction products formed in methods for producing single-wall carbon nanotubes (e.g., by carbon vaporization).
It is also an object of the present invention to provide a new class of tubular carbon molecules, optionally derivatized with one or more functional groups, which are substantially free of amorphous carbon.
It is also an object of this invention to provide a number of devices employing the carbon fibers, nanotube molecular arrays and tubular carbon molecules of this invention.
It is an object of this invention to provide composite material containing carbon nanotubes.
It is another object of this invention to provide a composite material that is resistant to delamination.
A method for purifying a mixture comprising single-wall carbon nanotubes and amorphous carbon contaminate is disclosed. The method includes the steps of heating the mixture under oxidizing conditions sufficient to remove the amorphous carbon, followed by recovering a product comprising at least about 80% by weight of single-wall carbon nanotubes.
In another embodiment, a method for producing tubular carbon molecules of about 5 to 500 nm in length is also disclosed. The method includes the steps of cutting single-wall nanotube containing-material to form a mixture of tubular carbon molecules having lengths in the range of 5-500 nm and isolating a fraction of the molecules having substantially equal lengths. The nanotubes disclosed may be used, singularly or in multiples, in power transmission cables, in solar cells, in batteries, as antennas, as molecular electronics, as probes and manipulators, and in composites.
In another embodiment, a method for forming a macroscopic molecular array of tubular carbon molecules is disclosed. This method includes the steps of providing at least about 106 tubular carbon molecules of substantially similar length in the range of 50 to 500 nm; introducing a linking moiety onto at least one end of the tubular carbon molecules, providing a substrate coated with a material to which the linking moiety will attach; and contacting the tubular carbon molecules containing a linking moiety with the substrate.
In another embodiment, another method for forming a macroscopic molecular array of tubular carbon molecules is disclosed. First, a nanoscale array of microwells is provided on a substrate. Next, a metal catalyst is deposited in each microwells. Next, a stream of hydrocarbon or CO feedstock gas is directed at the substrate under conditions that effect growth of single-wall carbon nanotubes from each microwell.
In another embodiment, still another method for forming a macroscopic molecular array of tubular carbon molecules is disclosed. It includes the steps of providing surface containing purified but entangled and relatively endless single-wall carbon nanotube material, subjecting the surface to oxidizing conditions sufficient to cause short lengths of broken nanotubes to protrude up from the surface; and applying an electric field to the surface to cause the nanotubes protruding from the surface to align in an orientation generally perpendicular to the surface and coalesce into an array by van der Waals interaction forces.
In another embodiment, a method for continuously growing a macroscopic carbon fiber comprising at least about 106 single-wall nanotubes in generally parallel orientation is disclosed. In this method, a macroscopic molecular array of at least about 106 tubular carbon molecules in generally parallel orientation and having substantially similar lengths in the range of from about 50 to about 500 nanometers is provided. The hemispheric fullerene cap is removed from the upper ends of the tubular carbon molecules in the array The upper ends of the tubular carbon molecules in the array are then contacted with a catalytic metal. A gaseous source of carbon is supplied to the end of the array while localized energy is applied to the end of the array in order to heat the end to a temperature in the range of about 500xc2x0 C. to about 1300xc2x0 C. The growing carbon fiber is continuously recovered.
In another embodiment, a macroscopic molecular array comprising at least about 106 single-wall carbon nanotubes in generally parallel orientation and having substantially similar lengths in the range of from about 5 to about 500 nanometers is disclosed.
In another embodiment, a composition of matter comprising at least about 80% by weight of single-wall carbon nanotubes is disclosed.
In still another embodiment, macroscopic carbon fiber comprising at least about 106 single-wall carbon nanotubes in generally parallel orientation is disclosed.
In another embodiment, an apparatus for forming a continuous macroscopic carbon fiber from a macroscopic molecular template array comprising at least about 106 single-wall carbon nanotubes having a catalytic metal deposited on the open ends of said nanotubes is disclosed. This apparatus includes a means for locally heating only the open ends of the nanotubes in the template array in a growth and annealing zone to a temperature in the range of about 500xc2x0 C. to about 1300xc2x0 C. It also includes a means for supplying a carbon-containing feedstock gas to the growth and annealing zone immediately adjacent the heated open ends of the nanotubes in the template array. It also includes a means for continuously removing growing carbon fiber from the growth and annealing zone while maintaining the growing open end of the fiber in the growth and annealing zone.
In another embodiment, a composite material containing nanotubes is disclosed. This composite material includes a matrix and a carbon nanotube material embedded within said matrix.
In another embodiment, a method of producing a composite material containing carbon nanotube material is disclosed. It includes the steps of preparing an assembly of a fibrous material; adding the carbon nanotube material to the fibrous material; and adding a matrix material precursor to the carbon nanotube material and the fibrous material.
In another embodiment, a three-dimensional structure of derivatized single-wall nanotube molecules that spontaneously form is disclosed. It includes several component molecule having multiple derivatives brought together to assemble into the three-dimensional structure.
The foregoing objectives, and others apparent to those skilled in the art, are achieved according to the present invention as described and claimed herein.